java访问持久层技术的进化

１.　pojo（简单的java，直接访问DB）

A. 导入所需的jar包

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.PreparedStatement;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

B. 获取与数据库的链接

private static Connection getConn() {
    String driver = "com.mysql.jdbc.Driver";
    String url = "jdbc:mysql://localhost:3306/samp_db";
    String username = "root";
    String password = "";
    Connection conn = null;
    try {
        Class.forName(driver); //classLoader,加载对应驱动
        conn = (Connection) DriverManager.getConnection(url, username, password);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return conn;
}

C.拿着链接cnn去操做数据库获取PreparedStatement

private static Integer getAll() {
    Connection conn = getConn();
    String sql = "select * from students";
    PreparedStatement pstmt;
    try {
        pstmt = (PreparedStatement)conn.prepareStatement(sql);
        ResultSet rs = pstmt.executeQuery();
        int col = rs.getMetaData().getColumnCount();
        System.out.println("============================");
        while (rs.next()) {
            for (int i = 1; i <= col; i++) {
                System.out.print(rs.getString(i) + "\t");
                if ((i == 2) && (rs.getString(i).length() < 8)) {
                    System.out.print("\t");
                }
             }
            System.out.println("");
        }
            System.out.println("============================");
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return null;
}

２．spring jdbcTemplate（jdbc模板访问DB）

A. 配置数据源<bean>-applicationcontext.xml

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="username" value="root"></property>
        <property name="password" value="密码"></property>
        <property name="url" value="jdbc:mysql://localhost:3306/newtest"></property>
        <property name="driverClassName" value="com.mysql.jdbc.Driver"></property>
    </bean>

B. 配置链接池<bean>-applicationcontext.xml

<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"></property>
    </bean>

C. 注入java中并使用

@Autowired
private JdbcTemplate jdbcTemplate;

.....
String sql = "SELECT * FROM stu"
return jdbcTemplate.queryForList(sql);

3.   ORM技术框架（对象-关系映射技术）

    3.1 MyBatis(前身是iBatis)

       另见博客！：https://my.oschina.net/u/3697586/blog/1924307

    3.2 Hibernate

    3.3 JPA